Dark nebulae were once thought to be holes in the Milky Way. This viewpoint changed as astronomers such as E.E. Barnard started serious study of the dark areas and photography was developed as a useful tool to study the heavens. These pioneers discovered that dark nebulae were not holes in the Milky Way but obscuring interstellar dust clouds blocking our view. These dust clouds may be small, dusty star forming regions, or may be portions of larger dark lanes of galactic dust. Other dusty spiral galaxies clearly show similar dark lanes and patches.

Dark nebulae are among the most difficult objects for an observer to search out. Although many are large enough to be naked eye or binocular objects, they may be difficult because transparent skies away from city lights are needed. The dark nebulae “holes” are not visible unless the Milky Way itself is clearly present. Identification is sometimes challenging. Some large dark nebulae include smaller, darker patches with separate ID’s which may cause confusion.

Dark nebulae vary in how much they obscure the background stars. Many dark nebulae have a Lynds opacity number associated with them. The Lynds opacity scale is based on Palomar blue and red photographic plates rather than visible light, but does provide a method of describing the apparent density of dark nebulae. In this 1-6 scale, the most opaque dark nebulae are classed as opacity 6, and the least opaque as opacity 1.